The Eagle’s Nest site, situated in the wetlands of the James Bay Lowlands, first appeared problematic to develop: the lack of exposed bedrock posed obvious logistical and environmental challenges. Noront’s solution was to develop a subsurface mine plan in which much of the milling facilities would be housed in a series of underground chambers.

“We have a unique situation,” says Paul Semple, Noront’s COO, “and I think we’ve come up with an innovative solution.” For Eagle’s Nest, the subsurface mine plan is possible because of the high competency of the subsurface waste rock – a granodiorite – that is much stronger than concrete and can support large open chambers. The chambers themselves will vary in size, with the largest spanning 16 metres.

The waste rock created by these excavations will be used for roads, concrete and foundations for a base camp.

Producing its own aggregate also allows Noront to control certain logistical and economic risks. “It just made common sense on a lot of fronts,” says CEO Wes Hanson. “Ultimately, I think it’s going to be a cheaper means of construction.” Making larger underground chambers is much less expensive than transporting construction materials by plane or winter road; fewer materials are needed, and much of it is already on site.

“The milling equipment is generally anchored to bedrock,” explains Hanson, “so either you’re going to excavate the soft surface material down to bedrock – between three metres and 20 metres – or drive piles down to bedrock. And that can be a very expensive process. We’ve avoided that whole area of uncertainty by putting the significant loads underground.” Noront will also save additional operating costs with the underground mill running in a constant temperature environment. Total mine operating costs over the life of the underground mine will be $1 billion, or $97 per tonne of ore.

A textbook deposit

Eagle’s Nest is set to be one of the world’s lowest cost nickel mines, thanks in large part to the deposit itself, as it is a sulphide, rather than a laterite, deposit. “The lowest cost producers around the world have been the sulphide miners,” points out Semple. “And I think this is one of the great undeveloped nickel sulphide deposits anywhere in the world.” Although nickel sulphides account for the majority of nickel mined to date, these reserves are quickly being depleted. Most new mines around the world are tapping laterites, which, though more abundant, are proving to be challenging to produce nickel from. “The sulphide technology has been used for a long time,” says Semple. “It has none of the growing pains seen in laterite deposits.”

The shape of the deposit is particularly ideal as well; it is pillar-shaped and nearly vertical, roughly 200 metres long and 60 metres across. “If you were to give a first-year underground engineering student an assignment to draw a perfect underground mine,” says Hanson, “they’d probably draw something that looks very much like Eagle’s Nest.” The deposit’s geometry, along with the high competency of the surrounding rock, allow for a straight-forward mine plan and conventional vertical bulk mining techniques, using blasthole stoping.

“The bigger challenge,” says Hanson, “is arranging the underground chambers so that work in the mine doesn’t impact work in the mill.” The crushing, grinding and flotation circuits of the milling process must be isolated from the rest of the underground workings.

A low profile

On the surface, the only visible signs of the Eagle’s Nest project will be a year-round airstrip, a base camp, and a number of support and storage buildings, all of which will occupy less than 50 hectares. “We’ll have one of the smallest environmental footprints of any underground mine in the world,” highlights Hanson. “It’s one of the things that we are proud of.”